@Inflictor 

Hello

Hopefully I should be able to answer some of these for you..

can anyone suggest the best settings for the ax11000 as smart connect I'm told drops WiFi sometimes 

Not sure where you heard this but not aware of Smart Connect dropping users unless they lose signal.  Smart Connect is generally a good thing for home users.  Set one SSID (wifi name) and let the router determine what is best for the device, if distance and signal strength is low it will move you to the 2.4ghz to give you range - but it always preferes to move you to the 5Ghz where possible for speed and performance.   Personally, I would (and do) leave this enabled as it load balances the network better than you could manually.

We would need more information before we could suggest setting for you, this is very dependent on your airspace.

do I set range to 160mhz. And channels ?

Again this is dependent on our airspace and you would really need to do a scan and see what your neighbours are doing.  Setting for 160mhz in the 5Ghz range will flood 4x channels, say 36, 40, 44, 48 for example.  There is not much point doing this if your are going to be constantly fighting for airspace with other APs, in this case moving to the 153 range of channels (or DFS if your country allowed) would be better as these generally tend to be less used.  Its also worth noting that clients would have to support the full 160mhz range to be able to utilize this, what are your client devices and what is the wifi cards in them?  No point fighting over the full spectrum if its not use to you.

My recommendation is to install a wifi analyser on your phone or windows device, this will scan the airspace and tell you what is happening.   If you want to post the screenshots here we could advise you better then.   Remember to mention what networks are yours and note the most common wifi cards you have installed in the client devices.  Im happy to help you where possible

also,is it better to have different passwords for each WiFi ?

While this is not totally required, personally I would recommend it.   What SSIDs are you thinking of creating?